1. Field of the Invention
This invention relates to a coaxial cylinder rheometer for testing the rheological properties of highly viscous and/or thermally sensitive materials. More particularly, this invention concerns a coaxial cylinder rheometer having a very small (less than0.020 inches [0.0508 cm]) gap between the concentric cylinders and being capable of charging highly viscous (greater than 100,000 poise) and/or thermally sensitive materials, e.g., Polyvinyl Chloride, Polyurethane, etc., into the gap for testing.
2. Description of the Prior Art
U.S. Pat. No. 2,812,656 discloses a coaxial cylinder viscometer in which the fluid to be tested is forced into the gap between the cylinders by means of a syringe through a hole and/or holes in the outer cylinder. The patent teaches that a viscometer constructed according to its disclosure has investigated viscosities up to 9,000 centipoises (90 poise) although indicating that this upper limit does not necessarily represent the practical limit of the viscometer. Said patent specifically notes that one of five potential deviations may be caused by the presence of a hole or holes in the outer cylindrical surface of said viscometer. This specific problem is solved by Applicant's invention since the two parts of the outer cylinder have their inner surfaces axially aligned and come into contact to complete an uninterrupted inner surface of this outer cylinder when in its operational position. Also, said patent teaches introduction of the material to be tested into the gap between the cylinders from one point or one vertical location only around the entire circumference of said gap. This may cause the gap to be filled ununiformly and may tend to cause eccentricity of the outer cylinder and inner cylinder. Applicant's invention overcomes these problems by extruding the material into the gap between the cylinders around the entire circumference of the gap. Therefore, the gap is filled uniformly by a force system which tends to maintain concentricity of the outer cylinder and inner cylinder and may actually tend to correct for any eccentricity of the outer cylinder and inner cylinder.